With hybrid-electric vehicle (HEV) technology gaining by leaps and bounds in the passenger-vehicle market, suppliers and end-users in various commercial-vehicle segments also are examining closely the case for hybridization.

Ultimately, the argument for hybrid powertrains in commercial vehicles is even stronger than for passenger vehicles.

The potential for hybridization in the commercial-vehicle sector may be more attractive because the gains of enhanced fuel economy are magnified. Engineers at Eaton Corp.'s technical center in Galesburg, MI, say they are working on two equally promising paths of hybrid-technology development for commercial vehicles.

First is the now well-known HEV architecture, which uses a battery pack to store electricity generated when the vehicle decelerates, later to be used by an electric motor or motors to assist the vehicle's internal-combustion engine.

The second is hydraulic launch assist — HLA — that uses a hydraulic accumulator in place of an HEV's battery pack to store deceleration energy that subsequently is used to help with acceleration.

Two hybrid architectures could be perceived as competitive, and sources say HLA might have cost advantages. But Eaton officials say it's likely both hybrid technologies will prove effective for different parts of the commercial-vehicle market.

With its Fluid Power division, Eaton has experience with hydraulics and says HLA could deliver great efficiency and maintenance-cost reduction for vehicles with duty cycles comprised largely of frequent accelerating from rest, traveling a short distance, then stopping. Think garbage trucks or city transit buses.

Unlike an HEV system, which usually is designed to use power from the electric motor to augment the vehicle's internal combustion engine in a variety of operating situations, HLA is dedicated to one purpose: helping to launch a heavy vehicle from rest; there is no benefit in other driving situations.

For that reason, the technology likely is less attractive than full-range hybrids for delivery trucks or over-the-road haulers.

With the HLA system, “We saw some opportunities that were different from what HEV was going after,” says Eaton's Kevin Beaty, business unit manager-Hybrid Electric Powertrains.

Donald Alles, Eaton's manager-Global Marketing Services and Roadranger Marketing, says Eaton, the world's leading producer of transmissions for heavy trucks and the highest-volume North American maker of heavy-duty clutches, has experience and an organization ideally suited to develop both hybrid technologies.

Eaton is comprised of four business groups: Fluid Power, Automotive, Electrical and Truck. Developing hybrid systems for commercial vehicles leverages knowledge from each Eaton operating group. And in 2000, Eaton added Hybrid Electric Powertrain Systems as a new business unit in its Truck Electronic Systems Div.

Eaton in 2000 started to build a prototype HEV commercial truck and will supply hybrid “power pack” components, 6-speed manual transmission and other technology for a fleet of 20 HEV utility trucks on the road next summer. The U.S. military and the WestStart consortium will administer the pilot program.

Meanwhile, HLA's advantage for frequent start-stop vehicles is the high power density and high energy transfer rate of hydraulics, says Steven Nash, director-New Business Ventures for the company's Fluid Power Group.

Eaton's current HLA system can deliver up to 1,000 lb.-ft. (1,356 Nm) of torque and 380 hp to the driveshaft. Its storage capacity is 750 hp-seconds, and the system can propel a Class 8 truck to 22 mph (35 km/h) without engaging the IC engine.

The HLA system had a high-profile coming out party in January 2002, when it added powertrain intrigue to the unveiling of Ford Motor Co.'s Mighty F-350 Tonka concept at the Detroit Auto Show.

“The genesis of the project at Eaton started about four years ago,” says Nash, who adds the company developed HLA in collaboration with the U.S. Environmental Protection Agency and Ford to examine the potential of the technology for automotive use.

“It ultimately was driven commercially from Ford,” says Nash, adding Ford since has dropped HLA development.

Nash says the HLA system has been upgraded to reduce noise and vibration, control fluid leakage and increase efficiency. End-to-end efficiency — the total amount of kinetic-energy recovery that then can be delivered to the driveshaft — is about 70%, he says.

Apart from boosting fuel economy and cutting emissions, HLA presents advantages that address priorities of commercial fleets, including longer brake life and associated lower maintenance costs. Brakes can be replaced several times annually for a vehicle such as a garbage truck, which typically has a lifespan of 10 years.

That is one reason why Eaton is targeting garbage trucks and city transit buses as the best potential markets for HLA.

“We think there can be a 2-or 3-year payback time in those target applications,” says Nash, regarding the cost of HLA. He says Eaton engineers have studied the scalability of HLA systems for passenger vehicles, but admits, “We're shifting resources significantly to heavy vehicles.”

On the HEV path, Beaty says Eaton has shipped 18 HEV trucks to courier giant FedEx Corp., and two have been running routes in Sacramento, CA, since January.

The Eaton-developed and supplied HEV system uses a single low-speed, high-torque motor and a nickel-metal hydride (NiMH) battery pack to augment the truck's diesel engine.

Beaty says early performance of the HEV delivery trucks is encouraging: The system improves fuel economy by 45% and cuts particulate and oxides of nitrogen (NOx) emissions by 93% and 54%, respectively. The added perk is the HEV delivery truck is 16% faster than its standard-powertrain counterpart, from 0-60 mph (97 km/h).

Delivery rival United Parcel Service also is testing HEV delivery trucks and has had one in field service (with non-Eaton components) since 1999.

Beaty says greater scrutiny of lifetime costs, centered largely around replacement battery packs, now is demonstrating HEVs should cost no more than a conventional truck when the initial cost is amortized over the life of the vehicle.

At volume, he says, fleet operators who pay more for HEV trucks “will at least get your (their) investment back.” With an equal lifetime-cost basis, and considering the escalating price of fuel, he adds, adoption of HEV technology could be viewed as a “hedge against fuel-cost escalation,” in addition to the environmental benefits.

He says the next phase of commercial-truck HEV technology will hone in on a Dept. of Energy target — under its cost-sharing Advanced Heavy Hybrid Propulsion System program — of 100% fuel economy improvement by 2007.

But Beaty says a new wrinkle may make HEV systems even more attractive: potential to generate electricity onboard the vehicle. He says HEV conversion for over-the-road rigs and other commercial vehicles may get a boost “if onboard power (generation) has a significant value proposition.”

The trucking industry is exploring ways to cut the amount of time long-haul rigs spend idling while parked, for example. Idling — necessary to produce electricity to run comfort and convenience components for the driver — among other things, uses fuel and generates emissions.

HEVs' onboard battery packs could supply much of that power while allowing the IC engine to be shut down most of the time the truck is stationary.

Onboard power generation for commercial trucks also could provide other useful advantages, as proven by the above-mentioned 20-unit pilot fleet of HEV utility trucks hitting the road next summer.

Those utility trucks can travel into areas with downed power lines and provide temporary electricity, in addition to bringing the personnel and equipment necessary to fix the problem.